Call Expr::peel_drop_temps() from more places for more accurate suggestions

Author: estebank

src/librustc_typeck/check/demand.rs

@@ -109,6 +109,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                               allow_two_phase: AllowTwoPhase)
                               -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
         let expected = self.resolve_type_vars_with_obligations(expected);
+        let expr = expr.peel_drop_temps();
 
         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
             Ok(ty) => return (ty, None),

src/librustc_typeck/check/expr.rs

@@ -87,12 +87,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
+            let expr = expr.peel_drop_temps();
             self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
-
-            let expr = match &expr.kind {
-                ExprKind::DropTemps(expr) => expr,
-                _ => expr,
-            };
             extend_err(&mut err);
             // Error possibly reported in `check_assign` so avoid emitting error again.
             err.emit_unless(self.is_assign_to_bool(expr, expected_ty));

src/librustc_typeck/check/mod.rs

@@ -4216,20 +4216,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     pub fn suggest_mismatched_types_on_tail(
         &self,
         err: &mut DiagnosticBuilder<'tcx>,
-        expression: &'tcx hir::Expr,
+        expr: &'tcx hir::Expr,
         expected: Ty<'tcx>,
         found: Ty<'tcx>,
         cause_span: Span,
         blk_id: hir::HirId,
     ) -> bool {
-        self.suggest_missing_semicolon(err, expression, expected, cause_span);
+        let expr = expr.peel_drop_temps();
+        self.suggest_missing_semicolon(err, expr, expected, cause_span);
         let mut pointing_at_return_type = false;
         if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
             pointing_at_return_type = self.suggest_missing_return_type(
                 err, &fn_decl, expected, found, can_suggest);
         }
-        self.suggest_ref_or_into(err, expression, expected, found);
-        self.suggest_boxing_when_appropriate(err, expression, expected, found);
+        self.suggest_ref_or_into(err, expr, expected, found);
+        self.suggest_boxing_when_appropriate(err, expr, expected, found);
         pointing_at_return_type
     }
 

src/test/ui/if/if-no-match-bindings.stderr

@@ -2,7 +2,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:18:8
    |
 LL |     if b_ref() {}
-   |        ^^^^^^^ expected bool, found &bool
+   |        ^^^^^^^
+   |        |
+   |        expected bool, found &bool
+   |        help: consider dereferencing the borrow: `*b_ref()`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -11,7 +14,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:19:8
    |
 LL |     if b_mut_ref() {}
-   |        ^^^^^^^^^^^ expected bool, found &mut bool
+   |        ^^^^^^^^^^^
+   |        |
+   |        expected bool, found &mut bool
+   |        help: consider dereferencing the borrow: `*b_mut_ref()`
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -44,7 +50,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:24:11
    |
 LL |     while b_ref() {}
-   |           ^^^^^^^ expected bool, found &bool
+   |           ^^^^^^^
+   |           |
+   |           expected bool, found &bool
+   |           help: consider dereferencing the borrow: `*b_ref()`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -53,7 +62,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:25:11
    |
 LL |     while b_mut_ref() {}
-   |           ^^^^^^^^^^^ expected bool, found &mut bool
+   |           ^^^^^^^^^^^
+   |           |
+   |           expected bool, found &mut bool
+   |           help: consider dereferencing the borrow: `*b_mut_ref()`
    |
    = note: expected type `bool`
               found type `&mut bool`